Neural development has been well characterized in rodents. Multipotent cells which are nestin immunoreactive and capable of differentiating into astrocytes, neurons, and oligodendrocytes have been identified by multiple investigators at various stages of development. In addition to multipotent precursors, other more restricted precursors have also been identified. Different populations of cells can be distinguished by differences in culture conditions, self-renewal capability, as well as in their ability to integrate and to differentiate following transplantation.
Similar studies using human tissue are indicative of the existence of multiple types of neural precursors as well. Multipotent human neural stem cells (hNSCs) have been isolated from fetal and adult tissue (Chalmers-Redman et al. Neuroscience 1997 76:1121-1128; Svendsen et al. J. Neuroscience Methods 1998 85:141-152; Vescovi et al. Exp. Neurology 1999 156:71-83; Carpenter et al. Exp. Neurology 1999 158:265-278; Quinn et al. J. Neuroscience Res. 1999 57:590-602; Piper et al. J. Neurophysiology 2000 84:534-548). These cells give rise to glia and neurons, can be grown under different culture conditions, and show different growth factor requirements.
Human neuron restricted precursors have also been described (Piper et al. J. Neurophysiol. 2000 84:534-548). Piper et al. used E-NCAM immunoreactivity to isolate neuronal precursor cells while Goldman and colleagues used neuron specific promoters to isolate neuronal precursors (Roy et al. Nat. Med. 2000 6(3):271-7; Roy et al. J. Neurosci. Res. 2000 59(3):321-31; Wang et al. Dev. Neurosci. 2000 22(1-2):167-76). Human neuronal restricted precursor cells have been isolated from the adult ventricular zone and hippocampus as well as from fetal tissue at multiple stages of development. These cells differ from human neuroepithelial cells by their expression of early neuronal markers such as NCAM, alpha-1 tubulin and beta-III tubulin.
Proliferative adult human oligodendrocyte precursors have been isolated from adult human white matter (Prabhakar et al. Brain Res. 1995 672(1-2):159-69, Raine et al. Lab. Invest. 1981 45(6):534-46; Scolding et al. Neuroreport 1995 6(3):441-5; Scolding et al. Neuroscience 1999 89(1):1-4) using cell surface markers. Others have used promoter-reporter constructs to isolate oligodendrocytes and their precursors from fetal and adult tissue. A2B5 immunoreactivity has been utilized to isolate glial precursors that are capable of differentiating into astrocytes and oligodendrocytes (U.S. Pat. No. 6,235,527).
Quinn and colleagues (J. Neurosci. Res. 1999 57:590-602) describe a mixed population of multipotent stem cells that can become altered in their properties after prolonged culture. These cells have been suggested to be astrocyte restricted precursor cells. However, oligodendrocyte differentiation has not been tested. Further, no information on antigenic expression, cytokine dependence, response to growth factors, expression of GFAP/S100, or A2B5 is available. The cells of Quinn et al. were obtained by sequentially passaging multipotent stem cells from cultured human spinal cord tissue.
A putative astrocyte precursor cell has also been described by Barres et al. (J. Neurosci. 1999 19(3):1049-61). This cell was isolated from the optic nerve and its existence in any other part of the brain is unknown. This cell is A2B5 immunoreactive and thus resembles the oligodendrocyte precursor O2A. The cells can be distinguished from the O2A cells mainly by their failure to develop into oligodendrocytes under conditions in which the O2A cells readily generate oligodendrocytes. This cell is Pax-6-positive and dies when exposed to serum. Immunoreactivity with CD44 is unknown.
Siedman et al. (Brain Res. 1997 753(1):18-26) have also described an astrocyte cell line derived by immortalization of a glial precursor cell. Little information on this immortalized precursor cell is available and its antigenic characteristics and ability to differentiate into neurons have not been disclosed.